The present invention relates to the field of aeronautic propulsion. It concerns a system for changing the pitch of the blades of a propeller driven by a turbine engine and in particular means for adjusting the pitch of the blades. It also concerns a turbine engine equipped with a pitch-change system of this kind.
Pitch change or variable setting of the blade pitches of a turbine engine propeller is one of the ways of improving the performance and efficiency of turbine engines in different flight conditions.
Turbine engines such as turboprop engines having propulsion propellers that are for example contra-rotating are known, designated in English by the terms “open rotor” and “unducted fan”, meaning an engine having an unducted fan equipped with these pitch-change systems. Turboprop engines differ from turbojet engines in that they use a propeller outside the nacelle (unducted) instead of an internal fan. The pitch-change system may also be applied to a turboprop having a single propulsion propeller or it may be equally compatible with more than one propeller.
In an open-rotor turboprop engine such as that shown in FIG. 1, a gas generator portion and a propulsion portion are aligned and arranged in a fixed cylindrical nacelle 2 carried by the structure of the aircraft. The gas generator portion is arranged downstream of the propulsion portion. Of course, the gas generator portion may be arranged in front of the propulsion portion. The gas generator portion comprises, from upstream to downstream, a set of compressors 3, a combustion chamber 4 and a set of turbines 5. A jet nozzle 8 is arranged downstream of the gas generator. The set of compressors 3 may comprise two compressors, as shown in FIG. 1, or a single compressor, typically having multiple stages depending on the chosen architecture of the gas generator. The set of turbines 5 may comprise a high-pressure turbine and a low-pressure turbine as in the case of FIG. 1 or, in a variant not shown, a single turbine typically having multiple stages. The propulsion portion has a pair of coaxial contra-rotating propellers 6, 7, upstream and downstream respectively, which are driven in inverse rotation to one another by the low-pressure turbine of the set of turbines 5 via a mechanical transmission device 17. This mechanical transmission device 17, which is represented simply by a diagram, comprises, for example, an epicyclic reduction gearbox. The propellers 6, 7 extend substantially radially in relation to the transmission shaft outside the nacelle 2.
Generally, each propeller 6, 7 comprises a substantially cylindrical rotary casing 9 carrying a hub having an outer polygonal ring 10 received in a rotary manner around the longitudinal axis X of the turbine engine in the fixed nacelle 2. The hub has radial cylindrical compartments 11 distributed on its periphery around the longitudinal axis. Shafts having radial axes, in this instance perpendicular to the longitudinal axis of the turbine engine, rigidly connected to the roots 13 of the blades 14, are received in the compartments 11 of the polygonal ring and also traverse radial passages 30 of the rotary casing.
Propeller pitch-change systems are known from documents GB-A-578570, U.S. Pat. No. 1,990,814, and FR-A1-2973333.
An example of a system for changing the pitch of each propeller is also known from document WO2013/050704. In FIG. 2, this system 23A for changing the pitch of each propeller is installed in the core of the rotating portions of a turbine engine, such as that shown in FIG. 1, comprising, for example, a control cylinder 25A for driving the blade roots in rotation. The annular control cylinder 25A comprises a cylinder 27A mounted on a fixed casing 13A and a piston 29A connected to a link mechanism 26A which is connected to each shaft 47A having a radial axis. The cylindrical rotary casing 11A rotates about the fixed casing 13A. For this purpose, at least one bearing 12A is arranged between the fixed casing 13A and the rotary casing 11A. The displacement of the movable piston 29A as a consequence of the fluidic control of the control cylinder 25A produces the desired angular pivoting of the blades by the link mechanism 26A by causing the radial shafts 47A connected to the blades to pivot. The radial shafts 47A transform the force generated by the control cylinder 25A into a torque directly on the propeller module.
However, the pitch-change system requires the integration of multiple diverse parts consisting of transforming a power arriving from the fixed portion into a movement on the rotating portion of the turbine engine. In particular, these parts form part of multiple kinematic sub-assemblies which must be placed in a certain position relative to one another and so that they operate in accordance with their preset operating parameters. The manufacturing tolerances of each part lead to problems in positioning the parts and plays, in particular axial plays, between the parts and the sub-assemblies. These manufacturing tolerances and plays affect the stroke of the control cylinder and in particular the setting of the blades. The setting of the blades may therefore be different on all the blades in a single propeller with a difference that is generally of the order of 0.5° relative to the expected setting. These problems of setting produce forces and vibrations that are detrimental to the operation and performance of the turbine engine.
The aim of the present invention is, in particular, to provide a pitch-change system that has a setting that is identical and true to the reference value across all the blades while being simple to manufacture, saving time during fitting, and taking into account the difficulties of integration into a congested environment.